Question

Formaldehyde gives an additive product with meth ylmagnesium iodide which on aqueous hydrolysis gives (a) methyl alcohol (b) isopropyl alcohol (c) propyl alcohol (d) ethyl alcohol

Short answer

The product is ethyl alcohol (d).

Step-by-step solution

Understanding the Reaction Components

First, identify the reactants involved in the reaction. We have formaldehyde (CH_{2}O) and methylmagnesium iodide (CH₃MgI), which is a Grignard reagent.

Grignard Reaction Mechanism

The Grignard reagent, CH₃MgI, reacts with formaldehyde. The methyl group (CH₃⁻) from methylmagnesium iodide attacks the carbon atom of the formaldehyde to form a new carbon-carbon bond, resulting in a magnesium alkoxide intermediate.

Formation of Magnesium Alkoxide Intermediate

The reaction \[ CH_3MgI + HCHO \rightarrow CH_3CH_2OMgI \] shows that the intermediate formed is ethyl magnesium iodide oxide.

Aqueous Hydrolysis of the Intermediate

By adding water (aqueous hydrolysis), the magnesium alkoxide intermediate is converted to an alcohol and magnesium hydroxide. The reaction is as follows: \[ CH_3CH_2OMgI + H_2O \rightarrow CH_3CH_2OH + Mg(OH)I \] This step releases ethyl alcohol (C₂H₅OH) as the product.

Key concepts

Formaldehyde

Formaldehyde is a simple organic compound with the formula \(CH_2O\). It is the simplest form of aldehyde. This compound is a colorless, pungent-smelling gas at room temperature but is often used in solution form. Formaldehyde is highly reactive, and this property makes it an important material in chemical synthesis.

In organic chemistry, formaldehyde is used to introduce the formyl group (\(–CHO\)) into target molecules. In the context of the Grignard reaction, formaldehyde serves as the electrophile. Here, the carbonyl carbon of formaldehyde is positively polarized, making it susceptible to nucleophilic attack by Grignard reagents.

Understanding formaldehyde’s role in this reaction is crucial. It acts as a building block that, when reacted with Grignard reagents like methylmagnesium iodide, forms larger organic molecules by creating new carbon–carbon bonds.

Methylmagnesium Iodide

Methylmagnesium iodide is a specific type of Grignard reagent with the formula \(CH_3MgI\). Grignard reagents are organomagnesium compounds used extensively in synthetic organic chemistry. They are notable for their ability to form carbon–carbon bonds. This characteristic is extremely valuable since it allows for the construction of larger, more complex organic structures.

Methylmagnesium iodide has a methyl group (\(CH_3^{-}\)) that acts as a nucleophile. In reactions, this methyl group actively seeks out electrophiles, such as the carbonyl carbon in formaldehyde, to form a bond. This nucleophilic attack is a hallmark of the Grignard reaction, which results in the formation of alcohols once the reaction is completed.

The interaction of methylmagnesium iodide with formaldehyde is a classic example of Grignard chemistry, where the aim is to build new molecules by creating strong carbon–carbon connections.

Magnesium Alkoxide

A magnesium alkoxide intermediate forms as a critical stage in the reaction process between formaldehyde and methylmagnesium iodide. Once the nucleophilic methyl group attacks the carbonyl carbon of formaldehyde, the result is a magnesium alkoxide compound. Specifically for this reaction, the intermediate formed is ethyl magnesium iodide oxide, represented by the formula \(CH_3CH_2OMgI\).

This stage is important as it represents the transition from initial reactants to the final alcohol product. The presence of magnesium in the intermediate indicates the compound is still bonded to the metal, and thus it is not yet the final alcohol form. It's the presence of this metal, magnesium, that makes the intermediate amenable to further chemical transformation through hydrolysis.

The magnesium alkoxide stage is key because it sets up the final steps needed to release the desired alcohol, proving the value of magnesium's role within this complex reaction transformation.

Aqueous Hydrolysis

Aqueous hydrolysis is the process of breaking down compounds using water. In the context of the Grignard reaction, aqueous hydrolysis is a critical step. It converts the magnesium alkoxide intermediate into the final alcohol product. This step involves adding water to the magnesium alkoxide, resulting in a chemical reaction.

During this step, the oxygen atom in water donates electrons, facilitating the removal of magnesium and the formation of an alcohol. For the reaction between formaldehyde and methylmagnesium iodide, this breakdown process releases ethyl alcohol (\(C_2H_5OH\)) as the final product. The hydrolysis also produces magnesium hydroxide as a byproduct.

Understanding this process is essential because it finalizes the transformation initiated by the Grignard reaction. It is the step that ensures the successful conversion of intermediate compounds to desired, usable chemical products. Aqueous hydrolysis is a fascinating step that highlights the intersection between simple water molecules and complex organic science.